BACKGROUND: Uterine fibroid is one of the most common pelvic neoplasms. It is rare for this condition to manifest as acute symptoms necessitating emergency surgical intervention.

CASE: A 46-year-old, Japanese woman was referred to our emergency room for sudden epigastric discomfort. A pelvic mass was felt, and computed tomography demonstrated a 13-cm hypodense multilocular cystic mass adjacent to the uterus. The anterior wall of the cyst was thinned and discontinued, suggesting rupture of the cyst. There was also massive ascites. Peritoneal irritation caused by rupture of an ovarian cyst was suspected, and an emergency exploratory laparotomy was performed. The patient was found to have a distended cystic mass protruding from the posterior surface of the uterus with 3,200 mL of blood-stained ascites. Closer examination revealed a 1-cm tear on the tumor surface, and both solid and cystic parts to the mass. Microscopically the tumor showed a proliferation of myometrial cells without atypia and hyaline degeneration. These findings were interpreted as a rupture of uterine fibroid after cystic degeneration.

CONCLUSION: Rupture of degenerated cystic fibroid is rare, but it should be included in the differential diagnosis when encountering patients with a cystic tumor and massive ascites.